1. Field of the Invention
This invention relates to radiation curable coating which is produced from a polyacrylate monomer and a vinyl monomer having an N-vinylimido grouping and, more particularly, to a tri- or tetraacrylate monomer in combination with an N-vinyl lactam monomer.
2. Description of the Prior Art
It is known that superior abrasion resistant coatings can be produced by thermal curing systems, but these suffer disadvantages, including the requirement to remove solvents and provide heat to process the coating which results in high costs for energy and air pollution control and eliminates their use on heat-sensitive materials. Thermal curing systems also do not lend themselves to rapid, continuous processing, as opposed to slow, batch processing, because of the requirement for heat and dwell time in the ovens to complete the cure and develop the superior abrasion resistance.
One hundred percent solids, radiation curing systems overcome the disadvantages of energy costs, solvent emissions, high temperatures, and slow batch processing associated with thermal curing systems. However, most radiation curing systems for abrasion resistant coatings developed up to this time have incorporated reactive polymers such as an urethane acrylate, together with various reactive monomers. These systems do not show the superior abrasion and chemical resistance properties of the best thermal curing systems.
Radiation curing systems using reactive monomer ingredients, without significant amounts of reactive polymers, are known which produce the desired superior abrasion and chemical resistance but these coatings are too brittle and produce too much curl for use on flexible substrates. Also, they exhibit poor adhesion on many substrates which, combined with their brittleness, results in undesirable cracking and peeling off from the substrate. In those cases where the existing monomer-based radiation curing coatings can be made to adhere to a rigid substrate without some type of adhesion failure, they exhibit slow radiation curing speeds and high viscosities which make rapid processing and smooth coating application difficult.